Hand scalers are used for removing dental calculus and the like, and have, for example, as shown in FIGS. 12 and 13, grip section 52 to be grasped by an operator, shank sections 53 provided on both ends of the grip section 52, and blade sections 54 located at the tip of the shank sections 53.
As shown in FIGS. 14 and 15, the blade section 4 of hand scaler 50 has sharpened cutting edges 54a, the tip of the blade section 54, i.e., toe 56 is formed rounded, and back face 54b is formed on the side opposite to the cutting edges 54a. The cutting edges 54a are used for scaling off dental calculus and the like, and the toe 56 is rounded so as not to hurt the dental gum upon accidental contact during the calculus removal.
The hand scaler having the blade section 54 with the rounded tip or toe 56 is called a curet hand scaler, while a hand scaler having a blade section with a pointed tip is called a sickle hand scaler.
Various types of curet and sickle scalers are available of which blade sections have different shapes of axes. For example, FIG. 14 illustrates a blade section 54 of a curet hand scaler, wherein the axis of the blade section extends in an arc shape. FIG. 16 illustrates a blade section 64 of a sickle hand scaler, wherein the axis of the blade section extends substantially straight. FIG. 17 illustrates a blade section 74 of another curet hand scaler, wherein the axis of the blade section is formed in an intermediate shape between a straight line and a mild arc. The blade sections 64 and 74 also have, like the blade section 54, cutting edges 64a, 74a and a back face 64b, 74b, respectively. The apex of the blade section 64 is pointed and called tip 66, whereas the apex of the blade section 74 is rounded to form toe 76.
As the hand scalers are used for removing calculus, their cutting edges become blunt due to abrasion, so that the edges have to be sharpened and repaired as necessary. Known apparatus for such repairing includes a manual type, wherein the grind stone is moved manually, and a motor-driven type, wherein the grind stone is moved by means of an electric motor or the like.
However, the conventional motor-driven apparatus has problems in that the blade tends to be ground excessively and prematurely worn, and that the apparatus is complex in structure and expensive. In order to prevent such excessive grinding of the blade, means have been proposed for adjusting the contact angle of the cutting edge to the grind stone. However, such adjusting means disadvantageously complex the apparatus structure and handling in maintenance. Thus a hand tool is demanded for easy re-sharpening of hand scalers in situ as desired.
For solving these problems, the present applicant proposed in JP-2001-38584-A a hand scaler sharpener apparatus including a sharpener main body having a grind stone capable of reciprocating, and a detachable attachment. This attachment includes a positioning plate for properly positioning a scaler tip on the grind stone, and having a notch formed in an arc shape substantially corresponding to the arc shape of the blade section of the hand scaler.
With the above-mentioned hand scaler sharpening apparatus, the hand scaler is held in hand, the back face of the blade section is pressed against the arc notch of the positioning plate, and the contact angle between the cutting edge of the blade section and the grind stone is adjusted under visual observation, while the grind stone is reciprocatingly driven. Thus the contact angle between the cutting edge and the grind stone may not be set properly, depending on the experience of the operator who does the sharpening.
In order to minimize such an error in the contact angle, the applicant further proposed in JP-2001-54840-A a hand scaler sharpening apparatus having an angle indication means in addition to the apparatus composition disclosed in the above JP-2001-38584-A. This angle indication means has angle indication lines or angle indication axes, and is positioned along the grind stone and the positioning plate. The operator presses the back face of the blade section of a hand scaler to the arc notch of the positioning plate, views the scaler against a background the angle indication means, and manually adjusts the angle of the scaler so that the axis of the shank section is in alignment with a particular background angle indication line or an angle indication axis, to thereby adjust the contact angle between the cutting edge and the grind stone.
The apparatus disclosed in JP-2001-54840-A indeed enables relatively accurate setting of the contact angle between the cutting edge and the grind stone, but the complexity in setting the contact angle is not sufficiently dissolved.